The objectives of the study are to evaluate the safety and tolerability of multiple oral doses of DMP777 administered at six dose levels and/or regimens, to determine pharmacokinetic and pharmacodynamic characteristics of multiple oral doses at each of these different dose levels and/or regimens, and to define dosage levels necessary to achieve sustained high-level systemic neutropil elastase inhibition. DMP777 is a potent inhibitor of PMN elastase located both within the azurophilic granules of viable cells and extracellularly following release at tissue sites of activation. DMP777 has been shown to have a high oral bioavailability which makes it an attractive compound for chronic administration central to the long-term management of CF lung disease.